a. Field of the Invention
This invention deals with the art of vision correction through the application of a soft contact lens to the human eye. More particularly, this invention details a novel method to dynamically alter the optical characteristics of a soft contact lens by changing the shape of the lens using a fluid disposed therein.
b. Description of the Prior Art
The human eye contains two main tissues or elements that act to focus light onto the retina. The cornea, which is the clear, watch crystal-like tissue on the outside of the eye, focuses light coming from distant objects. The ability to see distant objects is referred to herein as distance vision.
The other tissue or element is the crystalline lens on the inside of the eye (i.e., disposed radially inwardly from the cornea) that performs the Afocusing necessary to clearly image objects closer than approximately 20 feet, hereinafter referred to as near objects or near vision. The lens consists of concentric layers of protein arranged like an onion. In many people, and typically as a person ages, the lens gradually thickens and becomes less pliable. By the age of around 40, many people experience a condition known as presbyopia, which is characterized as a decreased ability to focus on near objects resulting from this thickening of the lens.
Historically, presbyopia has been addressed by prescribing spectacle lenses or glasses. These glasses are available in two forms: as reading lenses and, for people who have additional vision deficiencies such as myopia, as multifocal lenses. Reading glasses are appropriate to correct near vision. Their disadvantage is that a wearer must remove them in order to see clearly at distance. Glasses with multifocal lenses, including bifocal and progressive lenses, address both distance and near vision. These types of lenses provide correction by having lens portions with different focal points. Generally, an upper portion of the lens is adapted to correct for distance vision while a bottom portion is adapted for near vision. The person wearing the glasses adjusts their head so that they can gaze through the top portion to see far objects. In order to see near, they would keep their head as if they were looking at a distance then rotate their eyes downward so that they can gaze through the bottom portion in order to clearly focus on near objects. By changing the position of the eyes in the eye sockets, the wearers align their optical axes with different portions of the lenses. Multifocal lenses, including trifocals and progressives, may have additional portions to provide accurate focusing for objects at various intermediate distances from a wearer.
Some forty years ago, contact lenses (or contacts) started to be used as a common alternative to glasses to address both distance and near blurred vision. Two types of contact lenses are presently in use: Rigid Gas Permeable or hard contact lenses, and soft contact lenses. Hard contact lenses to correct distance vision generally are fit to partially rest under the upper lid and move with the lid during the blink. Translating bifocal hard contact lenses provide for correction for both distance and near vision, but work somewhat differently in that the lower edge of the contact rests against the lower lid so that as the wearer's gaze changes from a distant to a near object, the lens stays stationary at the lower lid while the eye rotates downward and gazes through the near vision portion of the contact. As a result, similar to glasses, as wearers move their eyes downward, they align their optical axes with different portions of the corrective hard contact lenses.
Soft contact lenses on the other hand drape on the cornea like a wet tee shirt and therefore remain essentially in the same location with respect to the optical axis of the eye, even during the blink. As a result, even as an eye moves, the contact lens effectively moves with it; therefore it effectively remains fixed relative to the eye's optical axis. This constant positioning insures that the optical axes of the contact lens and the natural lens of the eye coincide.
Such an approach presents a problem when one wants to create a bifocal soft contact lens because, no matter the direction of gaze, the visual axis of the eye always passes through the same portion of the lens. This problem is currently addressed by a contact lens that contains multiple refractive surfaces disposed directly along the visual axis. Examples of designs used for this purpose include aspheric, diffractive, concentric power rings, and refractive islands. All of these designs focus light coming from different distances onto the retina simultaneously. However, these designs all can result in “double or triple exposures” on the retina and can significantly degrade the quality of the retinal image, making such lenses unattractive to portions of the population. Therefore there is a need for an effective and user friendly multifocal contact lens.